Catalytic reduction of CO 2 to methane has been recognized as one of the most important strategic reactions to produce highly valuable chemicals and for storage of renewable energy (power-to-gas). This study demonstrates a crystal facet-dependent catalytic reduction of CO 2 to CH 4 on ruthenium nanoparticles deposited over TiO 2 nanocrystal with exposed (001) and (101) facets. Compared with TiO 2 (101) nanocrystal with the same Ru loading, Ru nanoparticles supported by TiO 2 (001) exhibited a highly enhanced CO 2 conversion rate and significantly improved methanation reactivity, along with a considerable durability. The physicochemical properties of the samples were characterized by HR-TEM, XRD, BET, FT-IR, UV–vis, Raman, ICP, and temperature-programmed reaction with CO 2 , and CO 2 + H 2 . In view of the difference in catalytic activity and the physicochemical properties of the supported Ru/TiO 2 catalysts, the results uncovered that the nature of the catalyst support of Ru/TiO 2 strongly affected the dispersion of Ru species and the synergistic effect between Ru and underlying TiO 2 supporting materials due to the strong metal-support interaction, and thus affected their capability to activate CO 2 and determined the catalytic activity for CO 2 methanation. Our work demonstrated the important role of the exposed crystal facets of the underlying support and the resulting Ru particle which had a large effect on CO 2 methanation.
Zhigang Wei,Yangfei Fang,Zhenrui Wang,Yue Liu,Yang Wu,Kai Liang,Jiahong Yan,Zhanchang Pan,Guanghui Hu
TiO 2 is one of the most cheap materials which can both adsorb arsenic and oxidize arsenite [As(III)] to arsenate [As(V)]. In this study, anatase TiO 2 crystals with different main facets such as {101}, {001} and {100} are synthesized and used to investigate arsenic adsorption kinetics, adsorption isotherms, photocatalytic oxidation (PCO) process and the pH effects. The adsorption kinetics of arsenic on TiO 2 crystals can be described by the pseudo second-order kinetic model. For the adsorption isotherms, the Langmuir model is better than the Freundlich model for arsenic on these TiO 2 crystals. For the PCO process, the rate of As(III) oxidation can be denoted by the pseudo first-order kinetic model. It should be noted that at neutral condition the adsorption and PCO rates of the three kinds of TiO 2 crystals follow the order of {101} > {001} > {100}. The pH effect is above all important for both the arsenic adsorption and its PCO. The highest PCO speed appears at high pH values such as at pH 11 or 12.
It is generally acknowledged that the crystal structure of the support plays a crucial role in the catalytic performance, however, the exact role of crystal structure in the catalytic system remains controversial. The Pd/TiO2 catalysts designed in this study with different crystals (rutile (r) and anatase (a)) were employed to study the effects of the crystal structure via a probe reaction for oxygen removal under a hydrogen atmosphere. Under the same reaction conditions, the temperature to achieve 90% O2 conversion on Pd/a-TiO2 could reach up to 150 °C, which is ∼1.4 times (107 °C) that of the Pd/r-TiO2 catalyst. Based on the various characterization results, it is found that strong metal support interactions (SMSIs) are dominant on the Pd/r-TiO2 catalyst, which could facilitate the formation of oxygen vacancies and Pd2+ species in the active sites, resulting in excellent catalytic performance. This study not only improves the understanding of the distinctive structural properties of TiO2 crystal support but also offers an effective strategy to design efficient heterogeneous catalysts via tuning SMSIs.
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